The following recommendations outline the common and most available ways to reduce energy consumption in compressed air systems. These suggestions include lowering operating pressure to the lowest level, implementing a reliable lead detection program, and utilizing proper controls to efficiently operate air compressors.
Reduce air pressure to the lowest possible level
Most industrial air equipment is designed to operate with 80 psi (or lower) air pressure. However, many compressed air systems are configured to produce air at 100 psi (or higher). For compressors operating around 100 psi, every 2 psi reduction in compressor discharge pressure results in a 1% reduction in compressor power. Additionally, by lowering system pressure, unwanted air losses from the system, including leaks, are reduced by 0.6% to 1.0%. This means that by reducing compressor discharge pressure by 2 psi, a 1.6% to 2.0% reduction in compressor power can be expected. The only implementation costs are the time for employees or contractors to adjust the system operating pressure, resulting in a short and reliable payback for this recommendation.
Implement a regular air leak detection and maintenance program
Generally, any fitting in a system can leak air, wasting energy required to produce the compressed air. Leaks can account for approximately 20% or more of the compressor’s flow output in an unmaintained system. For a well-maintained system, leaks can account for 10% of the total air flow. Regular checks of the compressed air system components will detect leaks before they become severe enough to adversely impact electricity costs or cause mechanical problems. Repairing air leaks can reduce the energy used by the compressed air system by 10% to 20%, thereby reducing costs to operate the system. Material costs for leak detection programs are relatively inexpensive. However, maintaining an air leak detection program can be extensive since the program requires frequent upkeep in order to have a positive impact on energy savings.
Improve end use efficiency
Compressed air systems should only be used for appropriate manufacturing processes as per the original design. Refraining from using compressed air systems for menial uses, such as tank sparging, cleaning off work spaces, and drying areas, avoids wasting energy. By removing unnecessary end uses, the compressors will require less power to compress the air. Various electrical devices can often be utilized to perform the same functions as the compressed air. Various equipment costs lead to various implementation costs, but often attractive and achievable paybacks can be realized.
Use automatic sequencer
Utilizing an automatic sequencer in a compressed air system coordinates the operation of all compressors in the system in order to maintain the desired system pressure. This ensures that the best combination of compressors is operating at all times and that only the necessary compressors are operating at any given time, resulting in a more efficient system. Automatic sequencers can also rotate the lead role in the compressed air system among each compressor, reducing uneven wear among system compressors. One caveat of the automatic sequencer is that the existing compressors must have sequencing capabilities, and sequencers must be available for the model of existing compressor. However, if the capability exists, typically 10% to 20% of the energy dedicated to the compressed air system can be saved by installing an automatic sequences. Automatic sequencers can require extensive initial costs, but can yield an attractive simple payback if the potential energy savings are substantial.
Recover compressor waste heat
The US Department of Energy estimates that as much as 80% to 93% of the electrical energy used by an industrial air compressor is converted into heat. Generally, if the waste heat is dissipated into the conditioned areas of the plant, HVAC costs can increase if the waste heat is large enough. The waste heat off the compressors can be recovered and utilized in other plant processes. HVAC savings are possible if the waste heat is used as space heating. A properly designed heat recovery unit can recover anywhere from 50% to 90% of the thermal energy released from the compressor. Typically, 5%-20% energy savings can be realized in an HVAC system if the waste heat is utilized. An attractive payback may also result if the HVAC system rework is not too extensive.
Reduce run time
Compressor systems are often left on overnight or left running when manufacturing processes are not using them. Significant amounts of energy can be wasted when systems are left running to keep compressed air at a higher pressure even when it is not needed. Compressors should be turned off at the end of every night shift during weekdays and during weekends if a facility is not in operation. Decreasing the run time of the compressors will reduce the energy usage and costs associated with operating the compressed air system. The implementation cost for this recommendation can be low since it only requires plant personnel to manually turn off the compressors, or simply the programming of sequencing systems to turn off the system at specified times.
The following recommendations describe further ways to reduce energy consumption and realize cost savings in a compressed air system. They include using the appropriate size and type compressor, as well as installing adequate air dryers.
Install compressor air intakes in the coolest location possible
As explained above, compressors are not completely efficient and can generate a significant amount of waste heat. Compressor work is directly proportional to the intake air temperature. On average, outside air is cooler and denser than indoor air. Therefore, by ducting outside air to the intake of the air compressor, energy savings may be realized. If compressors are housed in conditioned areas, the space conditioning energy requirements can also be reduced. Approximately 5% energy savings in the compressed air system or space conditioning systems can be observed by using cooler intake air for the compressors.
Utilize an optimum-sized compressor
A compressor's highest efficiency point is normally at full load. Therefore, optimum sized compressors should be used to create compressed air at the highest efficiency possible. Oversized compressors will either make too much air, to the point that it has to be regulated, or will operate at a low efficiency point. An undersized compressor simply will not meet the requirements of the compressed air system. A smaller compressor is not necessarily more efficient than a larger compressor, but as previously stated, a compressor's highest efficiency point is normally at full load. Therefore, an under-loaded (or oversized) compressor is inefficient at making compressed air. Optimum sized compressors should be chosen for the appropriate applications. Using optimum sized compressors can significantly reduce energy consumption of the compressed air system by up to 30% or 40%.
Use a dedicated compressor
Install an air compressor devoted specifically to a certain area if that area requires a higher a pressure than the rest of the system. As long as the compressor is capable of supplying the area requirements for machines to operate correctly, it will lighten the load for the system compressors. The dedicated compressor will allow the system compressors to operate at a lower discharge pressure or shut off during non-operating hours.
Install a VSD compressor
Variable speed drives (VSDs, or sometimes called variable frequency drives or VFDs) control the speed of a motor in an air compressor. The variable speed drives allow the motor to consume less power when less flow rate is needed instead of wasting excess energy through system losses. Therefore, using VSDs is a more efficient way to operate a compressor that operates under a variable load. Variable speed drives are also efficient operating as the trim compressor in a system. Up to approximately 10% of the energy in a compressed air system may be saved by utilizing a VSD compressor.
Install adequate moisture removal equipment
Air compressors intake air as it is, which almost always includes some humidity. By installing adequate dryers, most of the water content can be eliminated from the compressed air system, thereby keeping the system at its highest efficiency. Using efficient air dryers with appropriate capacity can yield potential cost savings, and a justifiable payback if implementation costs are reasonable.